Basic rules of population genetics.Understanding population genetics is an essential tool when comes to breeding and one that very few Leonberger breeders seem to take into account. The Institute of Canine Biology boasts some pretty impressive scientists on their team and they explain the fundamentals of population genetics:

1) All the useful genetic variation your breed ever had was in the dogs that founded the breed. This genetic diversity is finite, unless an out-cross is introduced.

2) Every generation, alleles are lost by chance (genetic drift) and also by artificial selection by breeders, who select for dogs with the traits they like, and remove other dogs from the breeding population.

3) Because the stud book is closed, genes that are lost cannot be replaced.

4) So, from the moment a breed is founded and the stud book is closed, loss of genetic diversity over time is inevitable and relentless.

5) You cannot remove a single gene from a population. You must remove an entire dog, and all the genes it has.

6) You cannot select for or against a single gene, because genes tend to move in groups with other genes. If you select for (or against) one, you select for (or against) them all.

7) Breeding for homozygosity of some traits breeds for homozygosity of all traits. Homozygosity is the kiss of death to the immune system. And as genetic variability decreases, so does the ability of the breeder to improve a breed through selection, because selection it requires variability.

8) The consequences of inbreeding (in all animals) are insidious but obvious if you look - decreased fertility, difficulty whelping, smaller litters, higher puppy mortality, puppies that don't thrive, shorter lifespan, etc. Genetically healthy dogs should get pregnant if mated. They should have large litters of robust puppies, with low pup mortality. Animals that cannot produce viable offspring are removed by natural selection.

9) Mutations of dominant genes are removed from the population if they reduce fitness. Mutations of recessive alleles have no effect unless they are homozygous. So rare alleles are not removed, and every animal has them.

10) Create a bunch of puppies that have a (previously) rare mutation, and the frequency of that bad allele in the population increases, so the chance of homozygosity increases.

11) Genetic disorders caused by recessive alleles don't "suddenly appear" in a breed. The defective gene was probably there all along. Make a zillion copies, and you have a disease.

12) Using DNA testing to remove disease genes will not make dogs healthier (see 2, 5, and 6).

13) The breed will continue to lose genes (by chance or selection) until the gene pool of the breed no longer has the genes necessary to build a healthy dog.

14) At this point, the breed might look beautiful (because of selection for type), but will suffer from the ill effects of genetic impoverishment. This includes increased cancer rates.

15) The only way to improve the health of a breed is to manage the health of the breed's gene pool.

16) The health of individual dogs cannot be improved without improving the genetic health of the population. Population genetics provides the tools for genetic management of populations of animals.

17) Breeders can improve the health of the dogs they breed if they understand and use the tools of population genetics.

18) Ultimately, the only way to increase the genetic diversity of a breed, and therefore its genetic health, is to carefully introduce new variations through carefully managed out-crossing, (e.g. from individuals who are completely outside the closed population). This is something that the UK Kennel Club and other breed registries are beginning to look at more closely.